Had your lease expired and you held over for 4 days or were you staying on indefinitely after the year was up? If #1, they can only charge you 4 days' holdover fees.
If #2, you are liable for the month's rent (inadequate notice) and for any late fees/penalties *authorized by law*. You will have to check your state's residential landlord-tenant act to see if the late fee/penalty terms from the expired 1 year lease apply to a subsequent month-to-month rental, or if the landlord is only entitled to the rent and/or statutory damages. You may also be entitled to a refund of any rent the landlord collects from the new tenant during the month for which you paid.
Regardless, the security deposit is another matter. The landlord can use it towards the money you owe if you don't pay, if any is left over after deducting for damages. If you pay the full rent and penalties, landlord has to refund your deposit.
NOTE: landlords cannot charge you for normal wear and tear (shampooing carpets once a year, painting every 1-2 years). You may also be entitled to interest on your deposit under local ordinance.
A good place to call is your local tenant's rights assiciation or landlord/tenant services.
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This is not legal advice and you are not my client. Double check everything with your own attorney and your state's laws.
[This message has been edited by Tracey (edited April 05, 2000).]